Since a vinyl chloride based resin is inexpensive and excellent in mechanical strength, weathering resistance, and chemical resistance, it has been used for various applications including building materials and housing materials. However, since the vinyl chloride based resin alone has no sufficient impact resistance strength, a method for adding a graft copolymer obtained by an emulsion polymerization or the like as an impact resistance modifier is currently widely used.
On the other hand, in recent years, in addition to the strength property such as impact resistance, appearance of a molded article such as surface gloss has been regarded to be important and particularly, in a window frame molded article, it has been strongly desired to satisfy both physical properties: that is, strength and gloss.
As a method for improving the impact resistance, disclosed is a method of adding, for example, a diene type or acrylate type soft rubber-containing graft copolymer.
Patent References 1 and 2 disclose graft copolymers containing graft components as shell parts and accompanying free polymers wherein the graft components are soluble in methyl ethyl ketone, insoluble in methanol in core-shell polymer compositions, and having a specific viscosity (ηsp) of 0.19 or higher measured at 30° C. in form of 0.2 g/100 ml acetone solution thereof, that is, polymer chains with high molecular weights; however they are techniques aiming to improve the weathering resistance, impact resistance, and secondary processability and the effect of improving gloss of a molded article is not mentioned, and these techniques are not sufficient as a method for satisfying both of gloss and impact resistance at high levels.
Patent Reference 3 discloses improvement of impact resistance by a graft copolymer containing, as a polyfunctional crosslinking agent, polyethylene glycol dimethacrylate having a main chain composed of —CH2—CH2—O— as a repeating unit; however Patent Reference 3 does not mention the effect of improving the gloss of a molded article, and similarly to Patent References 1 and 2, is not sufficient as a method for satisfying both of gloss and impact resistance at high levels, as described above, and also it cannot be said that impact resistance is sufficient.
A filler such as calcium carbonate is compounded to a vinyl chloride based resin composition for building fields and it is possible to improve the surface gloss to a certain extent by decreasing the compounding amount thereof; however it undesirably leads to rise of cost. Although the surface gloss can be improved also by increasing the molding temperature, there are many problems such as occurrence of thermal decomposition of vinyl chloride. Moreover, gloss can be improved by using, as a processing aid, a large quantity of a copolymer containing methyl methacrylate as a main component; however, the torque is increased due to the increase of melt viscosity and there is another problem of decrease of impact resistance.
That is, among conventionally known methods, there is not the method for improving both of gloss and impact resistance to high levels, which are particularly desired in recent years, and thus it has been desired to find the improvement method.
Accordingly, development of a graft copolymer satisfying both impact resistance and surface gloss has been desired.    Patent Reference 1: Japanese Patent Laid-open Publication No. 4-033907    Patent Reference 2: Japanese Patent Laid-open Publication No. 2002-363372    Patent Reference 3: Japanese Patent Laid-open Publication No. 7-3168